Noise from slotted rotors..?

[jaimz]

Hey dudes (and dudettes!)
I mentioned this in a different post some time ago, but I don't think it was quite the right thread.

I've got slotted and dimpled rotors on my VR-4 - made by Znoelli... probably not the best brand in the world, but it was what was recommended by a local garage, and well, they look sweeeet.
http://www.znoelli.co.nz/Discs_Sport.htm Mine are the DDS ones.

Since I had them fitted I'm noticing a 'ticking' sound coming from the wheels - it's especially noticeable when passing parked cars or along side a barrier where the noise is reflected back to me.

Does anyone else with slotted/driller rotors have the same thing..?

I had a talk to the dude at Ralliart at my last service and he said they shouldn't make a noise - and he deals with slotted rotors all the time in rally cars. (He even said they might be installed backwards and they the slots should 'sweep' forwards, rather than backwards, but I've don't know if I can question the competency of the garage I went to THAT much) Also, Freddy has the same rotors up front and said he hadn't noticed a noise either.

It seems feasible to me that noise could be produced from the quick compression and release of air in the slots and dimples as they pass in and out from behind the pad - like if you pass your finger back and forth in front of your mouth while blowing, but a) the fronts seem to be worse (or at least different) from the rears, and b) the noise is getting worse

So... any comments would be appreciated. Thanks.

[Nick Mann]

Any noise should only be apparent under braking, IMO. There is enough air noise going on that you shouldn't hear any ticking. Are you sure it is coming from the brake discs?

Grooves can go either way - it depends on the disc design. Check with the manufacturer or a dealer about fitting direction before you swap them round! I have had EBC discs, and found out that the previous owner had them fitted on the wrong sides. They did perform better and make less noise once swapped over.

[I-S]

If the noise happens as you're driving along then it could be the dust-guard behind the disc making contact with it (on mine it was a shiiiinkk-shiiiink-shhiiiiinnk noise).

If it's a clicking/cracking/rattling noise when braking (possibly also felt through the pedal on particularly loud ones) then it is missing anti-rattle plates on the back of the pads.

If it's an angle-grinder "Bzzzzzrrrrt" noise while braking, that's the disc and there's nothing you can do about it.

[Kenneth]

if it is a tap tap tap noise, also check your tyres for eithier stones or nails/screws in the tread area.

[jaimz]

Thanks guys.
It happens all the time (when travelling over about 30kph), and is really no worse under braking - there is a slight additional "shhhhhh" of pad on rotor, but the 'ticking' stays the same.

The thing that makes me think it's the rotors is that they ALL do it. All 4 of them. And it only started once the new rotors were installed. If it was something loose, or a little thing rubbing on something else, I'd have thought it would be an isolated case.

I think I'll go to the manufacturer and ask them. Will keep you posted.

Thanks for your help. Any further comments or epiphanies welcome :-)

[amsoil]

The slots should sweep backwards and yes I know some manufacturers mark them up the other way. If you think about it the slot is supposed to clean the surface away, and away on a rotating disc must be outward. Same applies to discs with curved vents.

[WildCards]

I realise it may be a different company, but does this help?



from here

[scc]

Same experience as Isaac's with the brake dust guard scrapping the disc itself.
Mine made a 'ssssshhhhh' noise on one of the wheels, and a 'shiiiiink'-'shiiiiink' noise on another.

My dust guard 'bent' forward whilst taking off the old discs. Used a gclamp to bend the dust guard back.

Cheers,
scc

[jaimz]

Cool. I'll get in and have a look.
Thanks guys.

[mitzylongboy]

i was just thinking.. is there any way you can jack up one or two of the wheels and get them spinning up and you watch to see if anything is interfering or causing rubbing? i'm not suggesting you put the car in gear and get them moving that way! mind you , you could go to a tyre/exhaust centre where they have those car lifter's that support the car in the middle and put it in gear to move the wheels like that? one last suggestion! if the sound is definately associated with the car in contact with the ground, maybe blagging a quick 20 minute sesion on your local dyno would help? the cost might be insignificant compared to the cost of any long term damage to you or your car? you can literally sit next to the wheels to see/hear whats happening? i just think that something like this can really start to wind you up and interfere with your driving ! speaking from experience with new breaks makind funny noises, it's better to hear it from outside as well as inside. i had a hell of a job sorting the breaks i fitted to my beetle ( i converted them from drums on the front ). good luck! i hope this might help? lol.